Sleep apnea-hypopnea syndrome (SAHS) has a high prevalence and is associated with adverse cardiovascular consequences in elderly veterans. Positive airway pressure therapy is deemed cumbersome and often associated with non-adherence to therapy. This proposal will investigate whether alternative therapies can be developed by modulating specific physiologic mechanisms of ventilatory control including chemoresponsiveness and cerebrovascular responsiveness. Specifically, we will study whether interventions with sustained hyperoxia (Aim 1), finasteride (Aim 2) and acetazolamide (Aim 3) will reduce breathing instability during sleep by reducing chemoresponsiveness and/or increasing cerebrovascular reactivity in order to alleviate sleep disordered breathing in elderly veterans with sleep apnea. The proposed aims will also allow us to delineate key mechanisms of breathing instability in the elderly. We envision that the results obtained from this project will ultimately allow us to develop novel alternative therapies for sleep apnea in elderly veterans.